Effects of wind turbine noise on songbird behavior during nonbreeding season

Anthropogenic noise is one of the fastest growing, globally widespread pollutants, affecting countless species worldwide. Despite accumulating evidence of the negative impacts of wind turbines on wildlife, little is known about how the noise they generate affects ecological systems. Songbirds may be susceptible to noise pollution due to their reliance on vocal communication and thus, in this field study, we examined how songbirds are affected by wind turbine noise. We broadcasted noise produced by one wind turbine in a migratory stopover site during the nonbreeding season. Throughout the study, we repeatedly monitored the acoustic environment and songbird community before, during, and after the noise treatments with passive acoustic monitoring and mist netting. We employed generalized linear mixed effects models to assess the impact of experimental noise treatment on birds behavior and likelihood ratio tests to compare models with variables of interest with null models. The daily number of birds in the presence of wind turbine noise decreased by approximately 30% compared with the before and after phases. This reduction had a significant spatial pattern; the largest decrease was closer to the speaker and on its downwind side, fitting measured sound propagation. Although we found no impact on species diversity, two out of three most common species showed clear avoidance behavior: 45% and 36% decrease in abundance for the lesser whitethroat (Sylvia curruca) and Sardinian warbler (Sylvia melanocephala momus), respectively. In the after phase, there were lingering effects on the lesser whitethroat. The age structure of the lesser whitethroat population was affected because only juvenile birds showed avoidance behavior. No difference in avoidance extent was found between migratory and nonmigratory species, but the impacts of displacement on migrants during stopover are especially troubling from a conservation perspective. Our results stress the need to address the impacts of noise pollution on wildlife when planning noise-generating infrastructures, such as wind turbines, to allow for sustainable development without threatening already declining songbird populations.

Neighbour-stranger discrimination in an African wood dove inhabiting equatorial rainforest

We investigated within- and between-individual song variation and song-based neighbour-stranger discrimination in a non-learning bird species, the blue-headed wood-dove (Turtur brehmeri), which inhabits lowland rainforests of West and Central Africa. We found that songs of this species are individually specific and have a high potential for use in individual recognition based on the time-frequency pattern of note distribution within song phrases. To test whether these differences affect behaviour, we conducted playback experiments with 19 territorial males. Each male was tested twice, once with the songs of a familiar neighbour and once with the songs of an unfamiliar stranger. We observed that males responded more aggressively to playback of a stranger's songs: they quickly approached close to the speaker and spent more time near it. However, no significant differences between treatments were observed in the vocal responses. In addition, we explored whether responses differed based on the song frequency of the focal male and/or that of the simulated intruder (i.e., playback), as this song parameter is inversely related to body size and could potentially affect males' decisions to respond to other birds. Song frequency parameters (of either the focal male or the simulated intruder) had no effect on the approaching response during playback. However, we found that the pattern of response after playback was significantly affected by the song frequency of the focal male: males with lower-frequency songs stayed closer to the simulated intruder for a longer period of time without singing, while males with higher-frequency songs returned more quickly to their initial song posts and resumed singing. Together, these results depict a consistently strong response to strangers during and after playback that is dependent on a male's self-assessment rather than assessment of a rival's strength based on his song frequency. This work provides the first experimental evidence that doves (Columbidae) can use songs for neighbour-stranger discrimination and respond according to a "dear enemy" scheme that keeps the cost of territory defence at a reasonable level.

Functional neurogenomic responses to acoustic threats, including a heterospecific referential alarm call and its referent, in the auditory forebrain of red-winged blackbirds

In animal communication, functionally referential alarm calls elicit the same behavioral responses as their referents, despite their typically distinct bioacoustic traits. Yet the auditory forebrain in at least one songbird species, the black-capped chickadee Poecile atricapillus, responds similarly to threat calls and their referent predatory owl calls, as assessed by immediate early gene responses in the secondary auditory forebrain nuclei. Whether and where in the brain such perceptual and cognitive equivalence is processed remains to be understood in most other avian systems. Here, we studied the functional neurogenomic (non-) equivalence of acoustic threat stimuli perception by the red-winged blackbird Agelaius phoeniceus in response to the actual calls of the obligate brood parasitic brown-headed cowbird Molothrus ater and the referential anti-parasitic alarm calls of the yellow warbler Setophaga petechia, upon which the blackbird is known to eavesdrop. Using RNA-sequencing from neural tissue in the auditory lobule (primary and secondary auditory nuclei combined), in contrast to previous findings, we found significant differences in the gene expression profiles of both an immediate early gene, ZENK (egr-1), and other song-system relevant gene-products in blackbirds responding to cowbird vs. warbler calls. In turn, direct cues of threats (including conspecific intruder calls and nest-predator calls) elicited higher ZENK and other differential gene expression patterns compared to harmless heterospecific calls. These patterns are consistent with a perceptual non-equivalence in the auditory forebrain of adult male red-winged blackbirds in response to referential calls and the calls of their referents.

Cognition mediates response to anthropogenic noise in wild Western Australian magpies (Gmynorhina tibicen dorsalis)

Anthropogenic noise is a pollutant of growing concern, with wide-ranging effects on taxa across ecosystems. Until recently, studies investigating the effects of anthropogenic noise on animals focused primarily on population-level consequences, rather than individual-level impacts. Individual variation in response to anthropogenic noise may result from extrinsic or intrinsic factors. One such intrinsic factor, cognitive performance, varies between individuals and is hypothesised to aid behavioural response to novel stressors. Here, we combine cognitive testing, behavioural focals and playback experiments to investigate how anthropogenic noise affects the behaviour and anti-predator response of Western Australian magpies (Gymnorhina tibicen dorsalis), and to determine whether this response is linked to cognitive performance. We found a significant population-level effect of anthropogenic noise on the foraging effort, foraging efficiency, vigilance, vocalisation rate and anti-predator response of magpies, with birds decreasing their foraging, vocalisation behaviours and anti-predator response, and increasing vigilance when loud anthropogenic noise was present. We also found that individuals varied in their response to playbacks depending on their cognitive performance, with individuals that performed better in an associative learning task maintaining their anti-predator response when an alarm call was played in anthropogenic noise. Our results add to the growing body of literature documenting the adverse effects of anthropogenic noise on wildlife and provide the first evidence for an association between individual cognitive performance and behavioural responses to anthropogenic noise.

Female red-winged blackbirds (Agelaius phoeniceus) do not alter nest site selection, maternal programming, or hormone-mediated maternal effects in response to perceived nest predation or brood parasitism risk

Predation or brood parasitism risks can change the behaviors and reproductive decisions in many parental animals. For oviparous species, mothers can mitigate their reproductive success in at least three ways: (1) by avoiding nest sites with high predation or parasitism risks, (2) through hormonal maternal effects that developmentally prime offspring for survival in risky environments, or (3) by investing less in reproduction when predation or parasitism risks are high. Here, we tested if perceived predation and parasitism risks can induce any of these behavioral or physiological responses by exposing female red-winged blackbirds (Agelaius phoeniceus) to playbacks of two major nest threats, a predator (Cooper's hawk, Accipiter cooperii) and an obligate brood parasite (brown-headed cowbird; Molothrus ater), as well as two controls (harmless Eastern meadowlark, Sturnella magna; and silence). We found that female blackbirds did not avoid nesting at sites treated with predator or brood parasite playbacks, nor were females more likely to abandon nesting attempts at these sites. Egg size and yolk hormone profiles, which are common proxies for maternal investment in oviparous species, were statistically similar across treatment sites. Instead, we found intraclutch variation in yolk steroid hormone profiles: concentrations of three progestogens (pregnanedione, 17α-hydroxypregnenolone, and deoxycorticosterone) and two androgens (testosterone and androstenedione) were higher in third-laid than first-laid eggs. Our study largely confirms previous findings of consistent intraclutch yolk hormone variation in this species, in birds in general, and in other oviparous lineages, but uniquely reports on several yolk steroid hormones largely overlooked in the literature on hormone-mediated maternal effects.

Using Acoustic Data Repositories to Study Vocal Responses to Playback in a Neotropical Songbird

Birds may alter song structure in response to territorial challenges to convey information about aggressive intent or fighting ability. Professional and amateur ornithologists upload daily many birdsong recordings into acoustic data repositories, usually scoring whether songs were recorded in response to a conspecific playback or produced spontaneously. We analyzed recordings from these repositories to evaluate if song traits of Rufous-browed Peppershrikes (Cyclarhis gujanensis) vary between playback-elicited songs and spontaneous songs. For each recording after playback, we chose one spatially closer spontaneous recording to avoid geographic bias. Birds recorded after playback produced slightly longer songs than birds that were singing spontaneously. This result was accounted for by increases in the amount of sound and silence within a song after the playback instead of changes in the mean number or duration of elements. Playback did not alter song frequency parameters (bandwidth, minimum, mean, and maximum frequencies) or song rate. These results indicate that song duration might mediate aggressive interactions in Rufous-browed Peppershrikes. Even considering limitations such as unknown playback stimulus identity and possible pseudoreplication, acoustic data repositories give a unique yet unexplored opportunity to gather insights into the evolution of song flexibility during aggressive encounters.

Methodological issues when using face prototypes: A case study on the Faceaurus dataset

Prototype faces, created by averaging faces from several individuals sharing a common characteristic (for example a certain personality trait), can be used for highly informative experimental designs in face research. Although the facial prototype method is both ingenious and useful, we argue that its implementation is associated with three major issues: lack of external validity and non-independence of the units of information, both aggravated by a lack of transparency regarding the methods used and their limitations. Here, we describe these limitations and illustrate our claims with a systematic review of studies creating facial stimuli using the prototypes dataset 'Faceaurus'. We then propose some solutions that can eliminate or reduce these problems. We provide recommendations for future research employing this method on how to produce more generalisable and replicable results.

Experimental evidence for core-Merge in the vocal communication system of a wild passerine

One of the cognitive capacities underlying language is core-Merge, which allows senders to combine two words into a sequence and receivers to recognize it as a single unit. Recent field studies suggest intriguing parallels in non-human animals, e.g., Japanese tits (Parus minor) combine two meaning-bearing calls into a sequence when prompting antipredator displays in other individuals. However, whether such examples represent core-Merge remains unclear; receivers may perceive a two-call sequence as two individual calls that are arbitrarily produced in close time proximity, not as a single unit. If an animal species has evolved core-Merge, its receivers should treat a two-call sequence produced by a single individual differently from the same two calls produced by two individuals with the same timing. Here, we show that Japanese tit receivers exhibit antipredator displays when perceiving two-call sequences broadcast from a single source, but not from two sources, providing evidence for core-Merge in animals.

It has been hypothesized that language depends on a capacity to produce and recognize two items (e.g., “come” + “talk”) as a single unit (e.g., “come talk”). Here, the authors show that a wild passerine also uses this capacity in vocal communication.

Female Aggression Towards Same-sex Rivals Depends on Context in A Tropical Songbird

Agonistic conflict is ubiquitous throughout taxa, although the intensity of aggression observed is often highly variable across contexts. For socially monogamous species, a coordinated effort by both pair members can improve both the chances of successfully warding off challengers and reinforce pair bonds. However, the intensity of aggression exerted by any one pair member may vary with respect to contextual factors, including the intensity of their mate's aggression. Thus, experimentally exploring how individuals respond to potential rivals via multiple assays with varying social contexts can advance our basic understanding of how aggression varies in socially monogamous systems. We used simulated territorial intrusion and mirror image simulation assays to explore this issue in white-shouldered fairywrens (Malurus alboscapulatus moretoni) of Papua New Guinea. While males tended to be more responsive than females during simulated territorial intrusions, females were more aggressive towards their mirrored reflection than males. Further, individual females that were most aggressive in mirror image simulations were the least aggressive during simulated territorial intrusions, whereas males were inconsistent. These results suggest that female behavioral phenotypes appear to be flexible, relative to context. We discuss how multiple commonly used measurements of aggression might in fact measure different types of responses.

Possible Event-Related Potential Correlates of Voluntary Attention and Reflexive Attention in the Emei Music Frog

Simple Summary

We investigated auditory event-related potentials (ERP) related to auditory attention in music frogs. Our objective was to explore whether ERP components related to voluntary attention and reflexive attention exist in frogs. We found that the amplitudes of stimulus preceding negativity (SPN, related to voluntary attention and under up-down control) evoked by silence replacement in the telencephalon were the largest when the sequence of acoustic stimuli could be predicted, while the N1 amplitudes (related to reflexive attention and under bottom-up control) evoked in the mesencephalon were the largest when the sequence of acoustic stimuli could not be predicted. This suggests that human-like ERP components related to voluntary attention and reflexive attention exist in the lower vertebrates also.

Abstract

Attention, referring to selective processing of task-related information, is central to cognition. It has been proposed that voluntary attention (driven by current goals or tasks and under top-down control) and reflexive attention (driven by stimulus salience and under bottom-up control) struggle to control the focus of attention with interaction in a push–pull fashion for everyday perception in higher vertebrates. However, how auditory attention engages in auditory perception in lower vertebrates remains unclear. In this study, each component of auditory event-related potentials (ERP) related to attention was measured for the telencephalon, diencephalon and mesencephalon in the Emei music frog (Nidirana daunchina), during the broadcasting of acoustic stimuli invoking voluntary attention (using binary playback paradigm with silence replacement) and reflexive attention (using equiprobably random playback paradigm), respectively. Results showed that (1) when the sequence of acoustic stimuli could be predicted, the amplitudes of stimulus preceding negativity (SPN) evoked by silence replacement in the forebrain were significantly greater than that in the mesencephalon, suggesting voluntary attention may engage in auditory perception in this species because of the correlation between the SPN component and top-down control such as expectation and/or prediction; (2) alternately, when the sequence of acoustic stimuli could not be predicted, the N1 amplitudes evoked in the mesencephalon were significantly greater than those in other brain areas, implying that reflexive attention may be involved in auditory signal processing because the N1 components relate to selective attention; and (3) both SPN and N1 components could be evoked by the predicted stimuli, suggesting auditory perception of the music frogs might invoke the two kind of attention resources simultaneously. The present results show that human-like ERP components related to voluntary attention and reflexive attention exist in the lower vertebrates also.

Evidence for acoustic discrimination in lemurs: a playback study on wild indris (Indri indri)

Indris (Indri indri) are group-living lemurs which occupy stable territories over several years and perform remarkable long-distance vocal displays. Vocal exchanges between long-term territory neighbours may contribute to assessing reciprocal resource holding potentials, thus adaptively reducing the costs of territorial defence by limiting aggressive escalation. Previous work showed that indris' songs show distinctive acoustic features at individual and group level. However, the possibility that indris use such cues for individual or group-level recognition has never been investigated experimentally. We conducted a playback experiment to test whether indris discriminate between familiar and non-familiar songs. Our rationale lies in the hypothesis of the dear enemy phenomenon, which predicts that territorial animals will show reduced aggression levels towards familiar neighbours compared to novel rivals. We played back stimulus recordings to wild indris from their territory boundaries and examined their responses in terms of vocal and behavioural indicators of willingness to engage in a fight. In line with our predictions, focal animals responded more rapidly and approached more often the speaker in response to playback stimuli of non-familiar individuals than to stimuli of neighbouring groups. These results indicate that indris can discriminate between different classes of intruders based on distinctive acoustic features of their song choruses. We suggest that increased aggression directed towards unfamiliar intruders may be explained by higher threat levels associated with dispersal and group formation dynamics. We further discuss the relevance of these findings in a strepsirrhine primate model for comparative studies of vocal communication and sociality.

Correlated evolution of distinct signals associated with increased social selection in female white-shouldered fairywrens

Conspicuous female signals have recently received substantial scientific attention, but it remains unclear if their evolution is the result of selection acting on females independently of males or if mutual selection facilitates female change. Species that express female, but not male, phenotypic variation among populations represents a useful opportunity to address this knowledge gap. White-shouldered fairywrens (Malurus alboscapulatus) are tropical songbirds with a well-resolved phylogeny where female, but not male, coloration varies allopatrically across subspecies. We explored how four distinct signaling modalities, each putatively associated with increased social selection, are expressed in two populations that vary in competitive pressure on females. Females in a derived subspecies (M. a. moretoni) have evolved more ornamented plumage and have shorter tails (a signal of social dominance) relative to an ancestral subspecies (M. a. lorentzi) with drab females. In response to simulated territorial intrusions broadcasting female song, both sexes of M. a. moretoni are more aggressive and more coordinated with their mates in both movement and vocalizations. Finally, M. a. moretoni songs are more complex than M. a. lorentzi, but song complexity does not vary between sexes in either population. These results suggest that correlated phenotypic shifts in coloration and tail morphology in females as well as song complexity and aggression in both sexes may have occurred in response to changes in the intensity of social selection pressures. This highlights increased competitive pressures in both sexes can facilitate the evolution of complex multimodal signals.

Discrimination of Acoustic Stimuli and Maintenance of Graded Alarm Call Structure in Captive Meerkats

Simple Summary

Preserving natural behaviors has many advantages for both research and animal welfare. Natural behaviors include producing vocalizations and responding to them. If it can be shown that the natural vocal repertoire is preserved in zoos, studies in zoos may help to expand the knowledge of acoustic behaviors and transfer it to animals in the wild. Once the meaning of diverse vocalizations is known, inferences can be made about an animal’s internal state in order to adapt and improve conditions for animals in zoos. In this paper, a natural and selective response of meerkats to potentially threatening acoustic signals such as the call of a predator is demonstrated. It can be shown that both the graded structure of meerkat alarm calls, which serves to convey the urgency of a dangerous situation, and the natural response to alarm calls are preserved. The obtained findings allow a continuation of the bioacoustic studies known for wild meerkats in zoos. The meerkat’s ability to already recognize acoustic signals as a potential threat may be crucial information for certain husbandry conditions. Vocalizing predators kept or naturally occurring near the meerkat enclosure form one example. The level of stress induced by potential threats and the associated alertness could be determined by using the graded alarm calls as a tool.

Abstract

Animals living in human care for several generations face the risk of losing natural behaviors, which can lead to reduced animal welfare. The goal of this study is to demonstrate that meerkats (Suricata suricatta) living in zoos can assess potential danger and respond naturally based on acoustic signals only. This includes that the graded information of urgency in alarm calls as well as a response to those alarm calls is retained in captivity. To test the response to acoustic signals with different threat potential, meerkats were played calls of various animals differing in size and threat (e.g., robin, raven, buzzard, jackal) while their behavior was observed. The emitted alarm calls were recorded and examined for their graded structure on the one hand and played back to them on the other hand by means of a playback experiment to see whether the animals react to their own alarm calls even in the absence of danger. A fuzzy clustering algorithm was used to analyze and classify the alarm calls. Subsequently, the features that best described the graded structure were isolated using the LASSO algorithm and compared to features already known from wild meerkats. The results show that the graded structure is maintained in captivity and can be described by features such as noise and duration. The animals respond to new threats and can distinguish animal calls that are dangerous to them from those that are not, indicating the preservation of natural cooperative behavior. In addition, the playback experiments show that the meerkats respond to their own alarm calls with vigilance and escape behavior. The findings can be used to draw conclusions about the intensity of alertness in captive meerkats and to adapt husbandry conditions to appropriate welfare.

Hierarchical auditory perception for species discrimination and individual recognition in the music frog

The ability to discriminate species and recognize individuals is crucial for reproductive success and/or survival in most animals. However, the temporal order and neural localization of these decision-making processes has remained unclear. In this study, event-related potentials (ERPs) were measured in the telencephalon, diencephalon, and mesencephalon of the music frog Nidirana daunchina. These ERPs were elicited by calls from 1 group of heterospecifics (recorded from a sympatric anuran species) and 2 groups of conspecifics that differed in their fundamental frequencies. In terms of the polarity and position within the ERP waveform, auditory ERPs generally consist of 4 main components that link to selective attention (N1), stimulus evaluation (P2), identification (N2), and classification (P3). These occur around 100, 200, 250, and 300 ms after stimulus onset, respectively. Our results show that the N1 amplitudes differed significantly between the heterospecific and conspecific calls, but not between the 2 groups of conspecific calls that differed in fundamental frequency. On the other hand, the N2 amplitudes were significantly different between the 2 groups of conspecific calls, suggesting that the music frogs discriminated the species first, followed by individual identification, since N1 and N2 relate to selective attention and stimuli identification, respectively. Moreover, the P2 amplitudes evoked in females were significantly greater than those in males, indicating the existence of sexual dimorphism in auditory discrimination. In addition, both the N1 amplitudes in the left diencephalon and the P2 amplitudes in the left telencephalon were greater than in other brain areas, suggesting left hemispheric dominance in auditory perception. Taken together, our results support the hypothesis that species discrimination and identification of individual characteristics are accomplished sequentially, and that auditory perception exhibits differences between sexes and in spatial dominance.

Eavesdropping on Referential Yellow Warbler Alarm Calls by Red-Winged Blackbirds Is Mediated by Brood Parasitism Risk

Referential alarm calls that denote specific types of dangers are common across diverse vertebrate lineages. Different alarm calls can indicate a variety of threats, which often require specific actions to evade. Thus, to benefit from the call, listeners of referential alarm calls must be able to decode the signaled threat and respond to it in an appropriate manner. Yellow warblers (Setophaga petechia) produce referential “seet” calls that signal to conspecifics the presence of nearby obligate brood parasitic brown-headed cowbirds (Molothrus ater), which lay their eggs in the nests of other species, including yellow warblers. Our previous playback experiments have found that red-winged blackbirds (Agelaius phoeniceus), a species also parasitized by brown-headed cowbirds, eavesdrop upon and respond strongly to yellow warbler seet calls during the incubation stage of breeding with aggression similar to responses to both cowbird chatters and predator calls. To assess whether red-winged blackbird responses to seet calls vary with their own risk of brood parasitism, we presented the same playbacks during the nestling stage of breeding (when the risk of brood parasitism is lower than during incubation). As predicted, we found that blackbirds mediated their aggression toward both cowbird chatter calls and the warblers’ anti-parasitic referential alarm calls in parallel with the low current risk of brood parasitism during the nestling stage. These results further support that red-winged blackbirds flexibly respond to yellow warbler antiparasitic referential calls as a frontline defense against brood parasitism at their own nests.

Visual obstruction, but not moderate traffic noise, increases reliance on heterospecific alarm calls

Animals rely on both personal and social information about danger to minimize risk, yet environmental conditions constrain information. Both visual obstructions and background noise can reduce detectability of predators, which may increase reliance on social information, such as from alarm calls. Furthermore, a combination of visual and auditory constraints might greatly increase reliance on social information, because the loss of information from one source cannot be compensated by the other. Testing these possibilities requires manipulating personal information while broadcasting alarm calls. We therefore experimentally tested the effects of a visual barrier, traffic noise, and their combination on the response of Australian magpies, Cracticus tibicen, to heterospecific alarm calls. The barrier blocked only visual cues, while playback of moderate traffic noise could mask subtle acoustic cues of danger, such as of a predator’s movement, but not the alarm-call playback. We predicted that response to alarm calls would increase with either visual or acoustic constraint, and that there would be a disproportionate response when both were present. As predicted, individuals responded more strongly to alarm calls when there was a visual barrier. However, moderate traffic noise did not affect responses, and the effect of the visual barrier was not greater during traffic-noise playback. We conclude that a reduction of personal, visual information led to a greater reliance on social information from alarm calls, confirming indirect evidence from other species. The absence of a traffic-noise effect could be because in Australian magpies hearing subtle cues is less important than vision in detecting predators.

Acoustically eavesdropping bat predators take longer to capture katydid prey signalling in aggregation

Prey that are signalling in aggregation become more conspicuous with increasing numbers and tend to attract more predators. Such grouping may, however, benefit prey by lowering the risk of being captured because of the predator's difficulty in targeting individuals. Previous studies have investigated anti-predatory benefits of prey aggregation using visual predators, but it is unclear whether such benefits are gained in an auditory context. We investigated whether katydids of the genus Mecopoda gain protection from their acoustically eavesdropping bat predator Megaderma spasma when calling in aggregation. In a choice experiment, bats approached calls of prey aggregations more often than those of prey calling alone, indicating that prey calling in aggregation are at higher risk. In prey capture tasks, however, the average time taken and the number of flight passes made by bats before capturing a katydid were significantly higher for prey calling in aggregation than when calling alone, indicating that prey face lower predation risk when calling in aggregation. Another common anti-predatory strategy, calling from within vegetation, increased the time taken by bats to capture katydids calling alone but did not increase the time taken to capture prey calling from aggregations. The increased time taken to capture prey calling in aggregation compared with solitary calling prey offers an escape opportunity, thus providing prey that signal acoustically in aggregations with anti-predatory benefits. For bats, greater detectability of calling prey aggregations is offset by lower foraging efficiency, and this trade-off may shape predator foraging strategies in natural environments.

Collective behaviour of the European minnow (Phoxinus phoxinus) is influenced by signals of differing acoustic complexity

Collective behaviour, such as shoaling in fish, benefits individuals through a variety of activities such as social information exchange and anti-predator defence. Human driven disturbance (e.g. anthropogenic noise) is known to affect the behaviour and physiology of individual animals, but the disruption of social aggregations of fish remains poorly understood. Anthropogenic noise originates from a variety of activities and differs in acoustic structure, dominant frequencies, and spectral complexity. The response of groups of fish may differ greatly, depending on the type of noise, and how it is perceived (e.g. threatening or attractive). In a controlled laboratory study, high resolution video tracking in combination with fine scale acoustic mapping was used to investigate the response of groups of European minnows (Phoxinus phoxinus) to signals of differing acoustic complexity (sinewave tones vs octave band noise) under low (150 Hz) and high (2200 Hz) frequencies. Fish startled and decreased their mean group swimming speed under all four treatments, with low frequency sinewave tones having the greatest influence on group behaviour. The shoals exhibited spatial avoidance during both low frequency treatments, with more time spent in areas of lower acoustic intensity than expected. This study illustrates how noise can influence the spatial distribution and social dynamics within groups of fish, and owing to the high potential for freshwater aquatic environments to be influenced by anthropogenic activity, wider consequences for populations should be further investigated.

Body size, habitat quality, and territory defense in Bachman’s sparrow

Many wild populations of animals conform to the ideal despotic distribution (IDD) in which more competitive individuals exclude less competitive individuals from high quality resources. Body size and aggressiveness are two important traits for resource defense, and they positively covary so that larger individuals are usually more aggressive. Using Bachman’s sparrows, we tested the hypothesis that larger birds are more aggressive and are thus able to compete for the best quality territories. We found that larger males were more aggressive, and more aggressive birds fledged at least one young. However, we did not find consistent relationships between aggressiveness and habitat characteristics. Our results suggest that Bachman’s sparrows meet most of the predictions of the IDD. Frequent ecological disturbances, such as fires, might disrupt the IDD or make it difficult to detect. Additional studies are needed to test for relationships between ecological disturbances and territorial behaviour.

Human Bone Proteomes before and after Decomposition: Investigating the Effects of Biological Variation and Taphonomic Alteration on Bone Protein Profiles and the Implications for Forensic Proteomics

Bone proteomic studies using animal proxies and skeletonized human remains have delivered encouraging results in the search for potential biomarkers for precise and accurate post-mortem interval (PMI) and the age-at-death (AAD) estimation in medico-legal investigations. The development of forensic proteomics for PMI and AAD estimation is in critical need of research on human remains throughout decomposition, as currently the effects of both inter-individual biological differences and taphonomic alteration on the survival of human bone protein profiles are unclear. This study investigated the human bone proteome in four human body donors studied throughout decomposition outdoors. The effects of ageing phenomena (in vivo and post-mortem) and intrinsic and extrinsic variables on the variety and abundancy of the bone proteome were assessed. Results indicate that taphonomic and biological variables play a significant role in the survival of proteins in bone. Our findings suggest that inter-individual and inter-skeletal differences in bone mineral density (BMD) are important variables affecting the survival of proteins. Specific proteins survive better within the mineral matrix due to their mineral-binding properties. The mineral matrix likely also protects these proteins by restricting the movement of decomposer microbes. New potential biomarkers for PMI estimation and AAD estimation were identified. Future development of forensic bone proteomics should include standard measurement of BMD and target a combination of different biomarkers.

Wild great tits' alarm calls prompt vigilant behaviours in free-range chickens

The ability to use heterospecific alarm calls is adaptive in the wild, as it provides an opportunity to avoid predators. We now know that several species are able to respond to alarm calls intended for others. However, this capacity has never been investigated in domestic animals. The capacity to use heterospecific alarm calls may be relevant for free-range domestic species, especially when they share predators with wild signallers. Using playback experiments, we investigated the vigilance behaviour of free-range naked neck chickens (Gallus gallus domesticus) when confronted with alarm calls (test playbacks) and songs (control playbacks) of a commonly occurring wild passerine, the great tit (Parus major). We found that subjects exhibited an increased vigilance to alarm calls compared to songs, therefore, showing that chickens respond to heterospecific signals as wild birds do. Recently, there has been an increased interest for free-range poultry production, notably because of the benefits of this farming method for chicken welfare. Although future studies are required to address this question, mortality due to predation may be reduced through the implementation of structures in areas frequented by wild heterospecific signallers.

Adjusted phonotactic reactions to sound amplitude and pulse number mediate territoriality in the harlequin poison frog

The information content of signals remains one of the central questions in animal communication. Auditory signals might contain information that allows receivers to estimate the distance as well as the size or the motivational state of senders. Proper differential reactions by receivers could be especially important for territorial species and lead to behavioural adjustments towards intruders according to the threat level: the perceived risk of losing territory. Therefore, territorial individuals should decode signal parameters that indicate the sender's size, distance, and motivation/treat level, reacting accordingly. To test this hypothesis, we studied the phonotactic reaction in territorial males of the poison frog Oophaga histrionica, after analyzing the variability of spectral and temporal parameters of natural calls. Next, we constructed synthetic calls by manipulating sound amplitude (sound pressure level: SPL), gross (inter-call intervals), and fine-temporal (number of pulses) structure of synthetic signals. In this way, we simulated near and far intruders with potentially variable sizes, motivational states, or threat levels. Then, we conducted playback experiments using these synthetic calls to determine 1) how perceived proximity of vocal competitors (determined by SPL) affect the behavior of receivers, and 2) how variation in the temporal structure of calls (inter-call interval and call pulse number) impact the behavior of receivers. We also asked whether signals convey body-size related information by analyzing the relationship between call parameters and body size of the males receiving the experimental stimuli. Consistent with our hypothesis, males recognized the variations in the SPL of calls. Males attacking the simulated opponent increased the number of pulses per call, while those retreating, kept pulse number unchanged (a graded aggressive signal). On the other hand, despite call traits resulted as poor predictors of body size, both SPL and fine temporal call traits might aid to predict whether a contestant will attack an opponent. Our data demonstrate that males discriminate and use SPL to estimate the sender's distance and use the call's fine temporal traits and to adjust the competitive/aggressive reaction using bimodal signals. They further suggest that body size assessment is not always an important factor in vocally- mediated agonistic interactions.

Fears from the past? The innate ability of dogs to detect predator scents

Throughout the animal kingdom, antipredator mechanisms are an evolutionary driving force to enable the survival of species classified as prey. Information regarding a predator's location can be determined through chemosensory cues from urine, faeces, visual and/or acoustic signals and anal gland secretions; and in several lab and field-based studies it has been seen that these cues mediate behavioural changes within prey species. These behaviours are often linked to fear and avoidance, which will in turn increase the prey's survival rate. In many studies dogs (Canis lupus familiaris) have been used as a predator species, however, no research has addressed a dog's innate ability to detect predator scents, hence the rationale behind this study. We assessed the innate ability of the untrained domestic dog to detect faecal scents of wild Eurasian brown bear (Ursus arctos arctos) and European lynx (Lynx lynx). The study monitored 82 domestic dogs across the UK and Norway. The dogs were exposed to the two predator faecal scents from Eurasian brown bear and European lynx, a herbivore faecal scent of Eurasian beaver (Castor fiber) and water control. Measurements were taken upon the time spent within a 40 cm radius of each scent and changes in the dog's heart rate when within this 40 cm radius. We found dogs spent a decreased length of time around the predator scents and had an increased heart rate in relation to their basal heart rate. We conclude that dogs can innately sense predator scents of brown bear and lynx and elicit fear towards these odours, as shown through behavioural and physiological changes.

Heterospecific eavesdropping on an anti-parasitic referential alarm call

Referential alarm calls occur across taxa to warn of specific predator types. However, referential calls may also denote other types of dangers. Yellow warblers (Setophaga petechia) produce “seet” calls specifically to warn conspecifics of obligate brood parasitic brown-headed cowbirds (Molothrus ater), which lay their eggs in the warblers’ and other species’ nests. Sympatric hosts of cowbirds that do not have referential alarm calls may eavesdrop on the yellow warbler’s seet call as a warning system for brood parasites. Using playback presentations, we found that red-winged blackbirds (Agelaius phoeniceus) eavesdrop on seet calls of yellow warblers, and respond as much to seet calls as to cowbird chatters and predator calls. Red-winged blackbirds appear to eavesdrop on seets as warning system to boost frontline defenses on their territories, although they do not seem to perceive the warblers’ seets as a cue for parasitism per se, but rather for general danger to the nest.

Lawson et al. study the response of the redwinged blackbirds to referential alarm calls in other bird species. They show that the blackbirds eavesdrop on heterospecific warning calls of the yellow warbler related to the nest parasites and respond by boosting their defenses to general danger on their territories.

Developmental polychlorinated biphenyl exposure influences adult zebra finch reproductive behaviour

Polychlorinated biphenyls (PCBs) are worldwide chemical pollutants that have been linked to disrupted reproduction and altered sexual behaviour in many organisms. However, the effect of developmental PCB-exposure on adult passerine reproductive behaviour remains unknown. A commercial PCB mixture (Aroclor 1242) or an estrogenic congener (PCB 52) were administered in sublethal amounts to nestling zebra finches (Taeniopygia guttata) in the laboratory to identify effects of developmental PCB-exposure on adult zebra finch reproductive parameters. Results indicate that although traditional measures of reproductive success are not altered by this PCB dosage, PCBs do alter sexual behaviours such as male song and nesting behaviour. Males treated with PCB 52 in the nest sang significantly fewer syllables than control males, while females treated with Aroclor 1242 in the nest showed the strongest song preferences. PCB treatment also caused an increase in the number of nesting attempts and abandoned nests in the Aroclor 1242 treatment relative to the PCB 52 treatment, and offspring with control fathers fledged significantly earlier than those with fathers treated with Aroclor 1242. Behavioural differences between males seem to best explain these reproductive effects, most notably aggression. These findings suggest that sublethal PCB-exposure during development can significantly alter key reproductive characteristics of adult zebra finches, likely reducing fitness in the wild.

Direct and indirect effects of noise pollution alter biological communities in and near noise-exposed environments

Noise pollution is pervasive across every ecosystem on Earth. Although decades of research have documented a variety of negative impacts of noise to organisms, key gaps remain, such as how noise affects different taxa within a biological community and how effects of noise propagate across space. We experimentally applied traffic noise pollution to multiple roadless areas and quantified the impacts of noise on birds, grasshoppers and odonates. We show that acoustically oriented birds have reduced species richness and abundance and different community compositions in experimentally noise-exposed areas relative to comparable quiet locations. We also found both acoustically oriented grasshoppers and odonates without acoustic receptors to have reduced species richness and/or abundance in relatively quiet areas that abut noise-exposed areas. These results suggest that noise pollution not only affects acoustically oriented animals, but that noise may reverberate through biological communities through indirect effects to those with no clear links to the acoustic realm, even in adjacent quiet environments.

Shared transcriptional responses to con- and heterospecific behavioral antagonists in a wild songbird

The recognition of and differential responses to salient stimuli are among the main drivers of behavioral plasticity, yet, how animals evolve and modulate functional responses to novel classes of antagonistic stimuli remain poorly understood. We studied free-living male red-winged blackbirds (Agelaius phoeniceus) to test whether gene expression responses in blood are distinct or shared between patterns of aggressive behavioral responses directed at simulated conspecific versus heterospecific intruders. In this species, males defend territories against conspecific males and respond aggressively to female brown-headed cowbirds (Molothrus ater), a brood parasite that commonly lays eggs in blackbird nests. Both conspecific songs and parasitic calls elicited aggressive responses from focal subjects and caused a downregulation in genes associated with immune system response, relative to control calls of a second, harmless heterospecific species. In turn, only the conspecific song treatment elicited an increase in singing behavior and an upregulation of genes associated with metabolic processes relative to the two heterospecific calls. Our results suggest that aspects of antagonistic behaviors to both conspecifics and brood parasites can be mediated by similar physiological responses, suggestive of shared molecular and behavioral pathways involved in the recognition and reaction to both evolutionarily old and new enemies.